Rit Búvísindadeildar - 20.11.1995, Page 42

Field wilting of grass
- drying rate and chemical changes
Bjarni Guðmundsson og Ásdís Helga Bjarnadóttir
SUMMARY
The effect ofcutting time and thefirst treatment ofgrass on the drying rate and
chemical changes underfield wilting was studied in two experiments in the summer
ofl992. Weather contions were rather favourable. Cutting in the morning (10-11
AM) was compared with cutting in the evening (21-22 PM). Spreading time was 0,
3, 6 and 12 hours after cutting. The main conclusions are following:
• Effective drying timefor the grass in thefield wasfrom 9 AM to 21 PM, when the
saturation deficit of the air is largest. The drying rate can be expressed with the
equationy = a + bx, werey is the DM(%) of grass andx is the saturation deficit-
sum (kPaxtime) during the effective drying time. The b - coefficients (i.e. "drying
rate") for the evening-cut grass were higher than for the moming-cut grass. The
shorter the time between cutting and spreading, the higher were the b-coefficients.
• Buffering capacity (BC) ofthe grass at cutting was low: 18-33 mE/100 g DM. BC
was 9% lower in evening-cut grass than in moming-cut grass. In moming cut
grass, BC decreased during wilting up to 40-45% DM, whereafter it increased. On
the other hand, BC in evening-cut grass increased immediately after cutting. On
average, BC in evening-cut grass (-45%) was more than two times higher
(>45mE/l 00 g DM) than ofmoming-cut grass.
• Sugar content (WSC) ofthe grass changed insignificantly during field wilting, up
to 45% DM. DMD fell only by 2%, if the grass was spread immediately after
cutting. The results ofthese experiments indicate that better utilisation ofeffective
drying time can be achieved by cutting in the evening, as well as higher DMD and
sugar content at baling.
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